The present invention generally relates to semiconductor devices, and in particular to semiconductor devices using copper or copper alloy as a wiring or metallization material.
It is known that a metallization pattern of a large scale integrated circuit (LSI) diminishes in width as its integration density increases. Although aluminum (Al) metallization is widely used for semiconductor chips, its width for metallization is limited to the range of 0.5 to 0.6 .mu.m. This is because the electromigration increases occurs as the aluminum metallization pattern becomes narrower. For these reasons, the use of a metallic material of a high melting point such as molybdenum (Mo) or tungsten (W) in place of Al has been considered. However, the resistivity of Mo or W is approximately twice the resistivity of Al in bulk and is more in a thin film. Therefore, a need exists for a metallization material having high electromigration resistance and low resistivity.
Presently, copper (Cu) is being investigated for metallization of LSIs due to its better electromigration resistance and lower resistivity than Al. A conventional semiconductor device with copper metallization is designed so that a copper metallization film is directly deposited on an insulating film such as
silicon dioxide (SiO.sub.2) film which is deposited on a silicon (Si) substrate and over contact holes formed in the insulating film so as to be positioned on diffused layers formed in the Si substrate. The copper film is then patterned in accordance with a wiring pattern. The semiconductor device thus configured is then generally annealed at a high temperature on the order of 400.degree. C. or over in order to grow grains of Cu and thereby improve the electromigration resistance.
However, the conventional semiconductor device with Cu metallization film mentioned above has a disadvantage that reaction and interdiffusion between Cu in the metallization film and Si included in the substrate, or Cu in the metallization film and Si in the insulating film occur during a heat treating process such as annealing. This is because the Cu metallization film is directly in contact with the Si substrate at the through holes in the insulating film. Reaction and interdiffusion cause an increase in the contact resistance and degradation of the Cu metallization. For these reasons, a need exists for preventing the reaction and interdiffusion between Cu and Si.